It is often desirable to include color artwork and text in documents. Color can make a document more interesting and more informative. In addition, many software applications that prepare documents and artwork provide many mechanisms to specify color and effects using color.
Color specifications in a document typically use one of two types of color, process colors or spot colors. A process color is a color that that is specified and printed using a set of colorants that define a standard color space, such as red, green, and blue (RGB colors space) or cyan, magenta, yellow and black (CMYK color space). Spot colors are colorants that are specified and printed as individual inks.
In traditional print workflows, printing devices have little or no ability to preserve the color appearance of artwork using spot color inks that the printing device does not have, especially when the artwork contains overlapped colors. Either spot color is removed and replaced with process color before printing, typically without reliable knowledge of the final printing device, or the artwork is printed as-is with poor results.
Artwork using an arbitrary set of spot colors may be printed as-is. Using a page description language such as PostScript, with its ability to accept fallback color descriptions for unavailable inks, the appearance of unavailable spot colors can be preserved reasonably well, as long as they are used only as opaque objects with no color overlapping, and as long as the application that produced the artwork used fallback colors that are handled well by the final printing device. This approach has the advantage of keeping the artwork description portable, but the restrictions noted above are unacceptable for most real-world artwork.
Alternatively, the artwork may be preprocessed and converted to use process color equivalents only instead of the original spot colors before printing. The spots are simply replaced with process color equivalents. The process colors may or may not resemble the original spot color inks when printed, depending on how they were selected, and whether the artwork is printed on a device matching the assumed output color characteristics. Overlapped process color areas may or may not look somewhat similar to the overlapped spot colors, depending on the combination of process colors in the area.
Additionally, preprocessing in general may increase the file management overhead of print workflows, because the preprocessing step typically creates one or more significantly larger new files that may need to be managed.